The present invention relates to a solid-state image sensing apparatus and, more particularly, to a structure of a read transistor portion for reading a signal charge from a photoelectric conversion portion such as a photodiode.
In the field of a solid-state image sensing apparatus, there have been proposed numerous technologies related to a structure of an amplified MOS image sensor which consumes lower power than a CCD image sensor and also allows easy integration between a sensor portion and a peripheral circuit by using the same MOS process.
Referring to FIGS. 4 and 5, a description will be given to an example of a structure of a MOS image sensor shown in Patent Document 1. FIG. 4 is a top view showing a photoelectric conversion portion and a signal read portion in a conventional MOS image sensor. FIG. 5 is a cross-sectional view taken along the line Y1-Y2 of FIG. 4.
As shown in FIGS. 4 and 5, a signal storage portion (photodiode) 102 made of an N-type diffused layer for converting optical light to electric charge and storing the electric charge therein is provided within a P-well 101. A gate electrode 104 is provided over the P-well 101 in adjacent relation to the signal storage portion 102 such that a gate oxide film 103 is interposed between the gate electrode 104 and the P-well 101.
A drain region 105 made of an N-type diffused layer is further provided in a surface portion of the P-well 101 which is on the side opposite to the signal storage portion 102 when viewed from the gate electrode 104. On the other hand, a surface shield layer 106 made of a P-type diffused layer is provided in a surface portion of the P-well 101 which is located above the signal storage portion 102. An isolation portion 107 made of a STI (Shallow Trench Isolation) formed by cutting into a substrate encircles the signal storage portion 102, the drain region 105, and the surface shield layer 106.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2000-150847